In the manufacture of articles by press molding certain starting materials, it is often necessary that the starting material be compressed in a mold by means of a press, and that the compacted material be maintained in the mold while heat or other means is used to cure or set the material in the molded condition. In many cases, the mold and material is cooled prior to removal of the molded article from the mold.
Molding articles in such a manner is time consuming as appreciable lengths of time are often required to effect the curing or setting, and cooling where necessary, prior to removal of the molded article from the mold. To maintain the mold in the press for the full duration of the cycle leads to uneconomical employment of a press which is generally a costly item of capital equipment.
One solution to this problem which has been proposed is to provide separate mold assemblies which are closed in a press and then are held in the closed position while being removed from the press and being further treated for curing by heating and subsequent cooling etc. An endless series of molds can then be treated by a single press.
Starting materials of particular concern are those comprising a base or filler material mixed with a variety of bonding agents, natural and plastic materials which are to be cured, set or bonded under the action of heat and optionally pressure. In many cases, this is followed by cooling, at least where the bonding agent, natural or plastic material is of the thermo-plastic type. It is to be noted that the natural adhesive nature of the ligning and cellulose content of the vegetable fibers or the like can be employed to advantage. Thus peat or the like can be added if required.
Filler materials of particular interest are those which are fairly compressible such as sub-divided timber, grasses, straws, other vegetable matter, and the like, but the method and apparatus with which this invention is concerned is also applicable to less compressible filler materials, for example, sub-divided solid materials such as ores, rocks, minerals, earths and the like or even to other moldable materials.
It is the object of this invention to provide a method and apparatus for press molding articles of the general type envisaged above which will provide a satisfactory rate of production while employing a limited number of molding presses, in particular one or two.